The present invention relates to a method and a device for controlling a vehicle engine.
To control a vehicle engine, it is known to use an accelerator pedal mechanically connected to the butterfly of a carburetor in order to influence the flow of air entering the engine. For various reasons, especially associated with fuel savings, these mechanical controls have been replaced with electrical controls by means of which the position of the accelerator pedal is sensed and serves to influence an electric motor which acts on the air intake butterfly of the carburetor. In both cases, the driver directly controls the flow of air entering the engine and, consequently, the engine torque.
In more sophisticated versions, various engine operating parameters, for example ignition advance and injection, are controlled by means of a torque setpoint which corresponds to the position of the accelerator pedal. In such a device, the position of the accelerator pedal is interpreted by an electronic device in order to supply a torque setpoint value which, according to a theoretical model, allows the engine torque to be controlled.
It has been observed that there is no direct torque sensor on commercial vehicles, so that the torque is necessarily controlled in xe2x80x9copen loopxe2x80x9d, that is to say without verification of the value actually obtained, but by indirectly estimating, especially as a function of the flow of air consumed, the air pressure in the intake manifold or the air/fuel ratio used. Because of the imperfection of the theoretical model and of the resistive torques (error of +/xe2x88x92 10%), such a device may cause annoyances when driving, saturations or diversity of response.
The present invention aims to overcome these drawbacks. To this end, the present invention provides a device for controlling the engine of a vehicle comprising an accelerator pedal and an engine speed control circuit comprising in particular:
a circuit for closed-loop control of the engine speed,
a circuit for interpreting the position of the accelerator pedal, which supplies an engine speed setpoint to the circuit for closed-loop control of the engine speed depending on the position of the accelerator pedal,
a circuit for estimating loads external to the vehicle,
characterized in that it is provided with a circuit for estimating maximum speed which gives a maximum engine speed likely to be reached by the engine as a function of the estimate of external loads supplied by the circuit for estimating external loads and in that this maximum speed is supplied to the circuit for interpreting the position of the accelerator pedal and makes the engine speed setpoint vary independently of the position of the accelerator pedal, so as to reproduce some of the sensations usually felt by the driver when the engine is torque controlled.
By means of these provisions, the engine is controlled by speed and not by torque, which makes it possible to take into account accurate measurements of the speed, to overcome the effects of at least some of the resistive torques and to optimize the transients. Since the engine speed can be easily measured, the closed loop control can be accurate, robust and carried out with simple algorithms. Furthermore, the circuit for interpreting the position of the accelerator pedal modifies the speed setpoint to take into account the variations of loads external to the vehicle.
According to particular features, the speed setpoint is modified by taking the value of the maximum engine speed delivered by the circuit for estimating maximum speed as a maximum limit of the setpoint speed in the circuit for interpreting the position of the accelerator pedal. Using these provisions, the driver may feel the usual driving sensations. For example, when the vehicle approaches a hill, the speed setpoint decreases and gives the sensation that the resistive torque due to the hill causes a variation in the stabilized speed.
According to particular features, the device as briefly mentioned above comprises a circuit for generating auxiliary loads which supplies a signal representative of predetermined resistive loads internal to the vehicle, the circuit for interpreting the position of the accelerator pedal not altering the setpoint speed for said predetermined auxiliary loads. By virtue of these provisions, the driver avoids the driving annoyances which are usually felt when the loads internal to the vehicle vary, for example when an air conditioner starts to operate.
According to particular features, the device as briefly mentioned above comprises a means for switching between an economical driving mode and a sporting driving mode, the dynamics of converging toward a setpoint engine speed being different for said driving modes. By means of these provisions, the vehicle manufacturer or driver may select a behavior xe2x80x9cmoodxe2x80x9d for the vehicle.
According to particular features, the device as briefly mentioned above comprises a weighting means for weighting between an operating mode with modification of the engine speed setpoint as a function of external loads by the circuit for interpreting engine speed setpoint and an operating mode without this modification. By means of these provisions, the driver may choose whether or not the engine speed of his vehicle changes as a function of the slope of the road on which he is moving.
The present invention also provides a method of controlling the engine of a vehicle comprising an accelerator pedal and an engine speed control circuit comprising:
a step a) of detecting the position of the accelerator pedal,
a step b) of estimating loads external to the vehicle,
a step c) of interpreting the position of the accelerator pedal during which said position is associated with an engine speed setpoint,
a step d) of closed-loop control of the engine speed according to the speed setpoint established in step c),
characterized in that it comprises, between step b) and step c)
a step b1) of estimating a maximum speed likely to be reached by the engine as a function of the external loads estimated in step b)
and in that the engine speed setpoint established in step c) is modified, independently of the position of the accelerator pedal, by the maximum speed likely to be reached by the engine, determined in step b1), so as to reproduce some of the sensations usually felt by the driver when the engine is torque controlled.